feat(allowlist): coverage projection + applied-count + post-accept projection (#7a/#7b)

Cluster B, milestone #99. Backend for the allowlist tuning dashboard.

#7a: AllowlistService.coverage(tag_id, threshold) counts distinct images with
a prediction resolving to the tag (raw_name==tag.name OR (raw_name,category) in
the tag's aliases) scoring >= threshold — the gross candidate pool, mirroring
tasks.ml._confidence_for_tag resolution. list_all now carries applied_count
(grouped image_tag count) + coverage_count (at the row's threshold). New
GET /api/tags/<id>/allowlist/coverage?threshold= for the live what-if number.

#7b: /suggestions/accept + /alias return {allowlisted, tag_id, tag_name,
projected_count} (projection at the tag's threshold) instead of 204, so the UI
can show a non-blocking 'auto-applying to ~N images' toast. Apply still runs
async via apply_allowlist_tags — projected_count is an estimate.

Tests: coverage by threshold (direct + alias-with-category), list applied vs
coverage, coverage route (explicit/default/bad threshold), accept/alias payload
(newly-allowlisted vs already-on-list).

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01XCUHUGQLrBrkgyk1t49kpX

backend/app/api/allowlist.py

@@ -20,12 +20,37 @@ async def list_allowlist():
                 "tag_name": r.tag_name,
                 "tag_kind": r.tag_kind,
                 "min_confidence": r.min_confidence,
+                "applied_count": r.applied_count,
+                "coverage_count": r.coverage_count,
             }
             for r in rows
         ]
     )
 
 
+@allowlist_bp.route("/tags/<int:tag_id>/allowlist/coverage", methods=["GET"])
+async def coverage(tag_id: int):
+    """Live "at threshold T, a sweep would cover ~N images" projection for the
+    allowlist tuning dashboard. Defaults to the tag's stored threshold."""
+    raw = request.args.get("threshold")
+    async with get_session() as session:
+        svc = AllowlistService(session)
+        if raw is not None:
+            try:
+                threshold = float(raw)
+            except ValueError:
+                return jsonify({"error": "threshold must be a float"}), 400
+            if not (0 < threshold <= 1):
+                return jsonify({"error": "threshold must be in (0, 1]"}), 400
+        else:
+            row = await session.get(TagAllowlist, tag_id)
+            if row is None:
+                return jsonify({"error": "not on allowlist"}), 404
+            threshold = row.min_confidence
+        count = await svc.coverage(tag_id, threshold)
+    return jsonify({"count": count, "threshold": threshold})
+
+
 @allowlist_bp.route("/tags/<int:tag_id>/allowlist", methods=["GET"])
 async def get_one(tag_id: int):
     async with get_session() as session:

backend/app/api/suggestions.py

@@ -3,12 +3,31 @@
 from quart import Blueprint, jsonify, request
 
 from ..extensions import get_session
+from ..models import Tag, TagAllowlist
 from ..services.ml.allowlist import AllowlistService
 from ..services.ml.suggestions import SuggestionService
 
 suggestions_bp = Blueprint("suggestions", __name__, url_prefix="/api")
 
 
+async def _accept_payload(session, svc, newly_added: bool, tag_id: int) -> dict:
+    """Shape the accept/alias response. When accepting newly allowlists a tag,
+    include the coverage PROJECTION (at the tag's threshold) so the UI can show
+    a non-blocking "auto-applying to ~N images" toast — the actual apply runs
+    async via apply_allowlist_tags, so this is an estimate, not a post-hoc
+    count (#7)."""
+    payload = {"allowlisted": newly_added}
+    if newly_added:
+        tag = await session.get(Tag, tag_id)
+        row = await session.get(TagAllowlist, tag_id)
+        payload["tag_id"] = tag_id
+        payload["tag_name"] = tag.name if tag is not None else None
+        payload["projected_count"] = await svc.coverage(
+            tag_id, row.min_confidence if row is not None else 0.90,
+        )
+    return payload
+
+
 @suggestions_bp.route("/images/<int:image_id>/suggestions", methods=["GET"])
 async def get_suggestions(image_id: int):
     # ?min=<float> overrides the configured per-category thresholds so the typed
@@ -60,13 +79,15 @@ async def accept_suggestion(image_id: int):
         return jsonify({"error": "tag_id required"}), 400
     tag_id = body["tag_id"]
     async with get_session() as session:
-        newly_added = await AllowlistService(session).accept(image_id, tag_id)
+        svc = AllowlistService(session)
+        newly_added = await svc.accept(image_id, tag_id)
+        payload = await _accept_payload(session, svc, newly_added, tag_id)
         await session.commit()
     if newly_added:
         from ..tasks.ml import apply_allowlist_tags
 
         apply_allowlist_tags.delay(tag_id=tag_id)
-    return "", 204
+    return jsonify(payload)
 
 
 @suggestions_bp.route(
@@ -77,19 +98,24 @@ async def alias_suggestion(image_id: int):
     required = {"alias_string", "alias_category", "canonical_tag_id"}
     if not body or not required.issubset(body):
         return jsonify({"error": f"required: {sorted(required)}"}), 400
+    canonical_tag_id = body["canonical_tag_id"]
     async with get_session() as session:
-        newly_added = await AllowlistService(session).add_alias_and_accept(
+        svc = AllowlistService(session)
+        newly_added = await svc.add_alias_and_accept(
             image_id,
             body["alias_string"],
             body["alias_category"],
-            body["canonical_tag_id"],
+            canonical_tag_id,
+        )
+        payload = await _accept_payload(
+            session, svc, newly_added, canonical_tag_id,
         )
         await session.commit()
     if newly_added:
         from ..tasks.ml import apply_allowlist_tags
 
-        apply_allowlist_tags.delay(tag_id=body["canonical_tag_id"])
-    return "", 204
+        apply_allowlist_tags.delay(tag_id=canonical_tag_id)
+    return jsonify(payload)
 
 
 @suggestions_bp.route(